Strength Of Clay Research Articles

CPT‐Based Probabilistic Characterization of Undrained Shear Strength of Clay

Applying random field theory involves two important issues: the statistical homogeneity (or stationarity) and determination of random field parameters and correlation function. However, the profiles of soil properties are typically assumed to be statistically homogeneous or stationary without rigorous statistical verification. It is also a challenging task to simultaneously determine random field parameters and the correlation function due to a limited amount of direct test data and various uncertainties (e.g., transformation uncertainties) arising during site investigation. This paper presents Bayesian approaches for probabilistic characterization of undrained shear strength using cone penetration test (CPT) data and prior information. Homogeneous soil units are first identified using CPT data and subsequently assessed for weak stationarity by the modified Bartlett test to reject the null hypothesis of stationarity. Then, Bayesian approaches are developed to determine the random field parameters and simultaneously select the most probable correlation function among a pool of candidate correlation functions within the identified statistically homogeneous layers. The proposed approaches are illustrated using CPT data at a clay site in Shanghai, China. It is shown that Bayesian approaches provide a rational tool for proper determination of random field model for probabilistic characterization of undrained shear strength with consideration of transformation uncertainty.

Slope Stability of Embankments on Soft Soil Improved with Vertical Drains

The overloads of structures or embankments built on clayey soft ground are generally applied gradually, respecting a specific phasing. This phasing on construction allows the undrained shear strength of clay increasing over consolidation in order to avoid the risk of collapse during loading. In this work, the undrained shear strength of clay over the consolidation was estimated following SHANSEP method of which parameters proposed by eight researchers have been employed, as well as the slope stability analysis of embankments on soft soils during staged construction. Assessment of factor of safety for slope stability was conducted basing on the Bishop method. Additionally, the variations of undrained shear strength and factor of safety were presented. In order to validate the methods discussed in this study, slope stability analysis of five embankments constructed on clayey soft soils improved by the vertical drain technique in a high-speed railway construction project in Morocco was performed. For these embankments, field measurements about lateral displacement are presented. It was found that some of the adopted methods is in a good agreement with field measurements. Hence, generalization of these methods to many soft ground cases can be proposed.

Effect of Vertical Drains on Strength and Deformation Characteristics of Lithomargic Clay

During olden days, construction used to be carried out only on the sites having good strength. But now-a-days availability of sites with favourable properties are limited. So, there is a need to modify the properties of subsoil using different types of Ground Improvement Techniques. Depending upon the nature of soil, a suitable economical technique needs to be adopted. Soft soils have weaker strength and they are highly compressible and take a lot of time for settlement. So, these are typically problematic for construction. There is a need to improve the condition by accelerating the rate of consolidation. To achieve higher rate of consolidation, it is important to develop shorter paths for movement of the water. A vertical drainage system can be provided to accelerate the rate of consolidation and help to minimise excess pore pressure in the sub-soil. As a result of this, a stable situation is reached more quickly. Thus to enhance the strength of the soil and to accelerate the consolidation rate, vertical drains of different diameters and with varied spacing are employed. The improvement in properties of soft consolidating lithomargic clay is experimentally tested with vertical sand drains in developed prototype. The vertical sand drains installed with 1.905 (0.75 inch) diameter and 6 cm spacing is more effective in increasing Ultimate Bearing Capacity (UBC) of soil and also the rate of settlement of 35.26 % is significant up to 60 kg of preloads. Thus problematic lithomargic clay can be improved in its strength and settlement characteristics.

Assessment of Geo Technical Properties of Nano-Lime Treated Expansive Clay

In geotechnical engineering practice, expansive clay is widely encountered. It poses to be a serious problem especially in metropolitan areas by virtue of its low strength and high compressibility. Further, these soils undergo significant change in volume as a consequence of variation in the moisture content. Soil stabilisation is one such technique practiced to improve the shear strength and to control volume change in expansive clays. Among various stabilisation techniques, Lime has been found to be an effective stabilizer, which appreciably alters the properties of expansive clay. Further, the reaction will be very effective on the usage of nano size particles in the stabilisation of expansive clay. At the first step, the effect of lime stabilisation on geotechnical properties such as grain size distribution, index properties, compaction characteristics, differential free swell and unconfined compressive strength of expansive clay was studied by varying percentages of lime. At the second step, the effect of nano- lime on the properties of optimum soil-lime mixture was investigated. The percentage of nano- lime is varied from 0.25- 1.0% by dry weight of the soil. The measured results show that the use of nano- lime in expansive clay significantly improves its strength and reduces swell behaviour resulting in reduced pavement thickness.

Strength and Durability of Bottom Ash and Lime Stabilized Bangkok Clay

High rainfall is observed in a tropical climatic country like Thailand that results in higher chances of natural calamities like flood. High plastic clay known as Bangkok clay is present in Thailand. The clay is famous for displaying variability in its geotechnical properties under dry and wet conditions. Therefore, such clay must be treated with some other materials for the stability of roads along with vehicles running through them. Bottom ash that is one of the waste materials produced from coal combustion has been used for this study along with lime. Tests like unconfined compressive strength test, durability test has been conducted by determining the strength under dry and wet condition. Two methods of soaking have been adopted when performing wetting-drying namely complete and capillary soaking. The results showed improvement in strength as well as durability after replacement with bottom ash and lime. The strength of the soil specimen after treatment with bottom ash and lime has improved 2 -fold with 50% amount of bottom ash and 12% lime. The same ratio of materials: 50% bottom ash and lime with the clay showed the optimum amount in terms of durability.

Strength and Durability of Bottom Ash and Lime Stabilized Bangkok Clay

High rainfall is observed in a tropical climatic country like Thailand that results in higher chances of natural calamities like flood. High plastic clay known as Bangkok clay is present in Thailand. The clay is famous for displaying variability in its geotechnical properties under dry and wet conditions. Therefore, such clay must be treated with some other materials for the stability of roads along with vehicles running through them. Bottom ash that is one of the waste materials produced from coal combustion has been used for this study along with lime. Tests like unconfined compressive strength test, durability test has been conducted by determining the strength under dry and wet condition. Two methods of soaking have been adopted when performing wetting-drying namely complete and capillary soaking. The results showed improvement in strength as well as durability after replacement with bottom ash and lime. The strength of the soil specimen after treatment with bottom ash and lime has improved 2 -fold with 50% amount of bottom ash and 12% lime. The same ratio of materials: 50% bottom ash and lime with the clay showed the optimum amount in terms of durability.

Flotation of pipes and cables in consolidating backfill

This paper discusses the flotation of cables and pipelines that have been trenched using jet trenching during reconsolidation of the seabed soil. Utilising previously published data on the variation of clay strength with liquidity index, it is demonstrated for the first time that, while current industry guidance is appropriate for the low-plasticity clays for which much previous research has been carried out, it may be overly conservative for high-plasticity clays such as those found in the Gulf of Guinea or the Gulf of Mexico, owing to the differing strength and density characteristics of these soils.

Study of Fibre-Clay Interface Behaviour and Reinforcing Mechanism

The use of fibres in a random orientation within weak/problematic soils is one of the techniques for their improvement. In the recent past, some studies on fibre inclusion in soils at macro-level have been reported. However, the interaction between fibres and soil particles is still not very clear. In the present study, an attempt has been made to explain the response of an individual fibre when the fibre-reinforced specimen is subjected to shear. The comparative analysis between cement-coated and uncoated fibre was done to measure the change in interfacial shear strength of fibre and clay. The effect of different initial orientations of fibre was evaluated by performing the direct shear tests. As the placement of fibre at any specific orientation in compacted clay specimen is practically a very difficult task, the special equipment has been designed to prepare a fibre-clay specimen where a single fibre can be placed at any predefined orientation in compacted clay. The test result shows that the fibre-clay matrix develops high shearing resistance if fibre is oriented near to the horizontal surface. In comparison to the uncoated fibre, due to the development of cementitious bond, the clay specimen reinforced with cement-coated fibre achieves much higher interfacial strength.

Molecular-level simulations of oil-contaminated clays

Petroleum products, besides being the core of the energy source, frequently result in the contamination of subsurface soils. Clay minerals, being electrochemically active components of soils, are the most affected and hence lead to substantial change in behaviour and properties of the soils. This paper provides a multilevel study consisting of macro and micro testings coupled with molecular-level simulations of the behaviour of active clay mineral in the soil structure, pore fluids and dissolved salts when contaminated with crude oil. There was a significant change in the engineering behaviour of the contaminated clay. The coarse-grained soil-like behaviour was observed in the strength of the oil-contaminated clay. The contamination has affected the plasticity and the cation-exchange capacity of the investigated clay. The swelling pressure of the contaminated clay is reduced to about one third of that of the uncontaminated clay, while there was no change observed in the swelling percentage. The formation of oil-coated agglomerates due to the addition of the crude oil has been found to be responsible for most of the physical and mechanical processes in the contaminated clays. The study’s molecular-level simulation modelling concepts can be used to describe the behaviour of clay minerals and other interacting compounds.

Behaviour of the Undrained Shear Strength of Soft Clay Reinforced with Natural Fibre

The term soil reinforcement is conventional since decades ago for the stabilization of soft ground such as of clay and peat. Numerous research has arisen in the utilization of natural fibres as the reinforcement materials. Cost reduction, increment of sustainability awareness and eco-friendly environment are some of the advantages when using natural fibres to stabilize soft ground. A research study was carried out to evaluate the strength of the soft soil when unreinforced and reinforced using natural fibres. The findings on the experimental investigation of the study will be presented in this paper. Crushed coir fibres were used to reinforce an intermediate plasticity soft clay where both materials were collected locally in Brunei Darussalam. The crushed coir fibres were added at 0.5%, 1.0%, 1.5% and 2.0% to the dry weight of the sample. A series of an unconsolidated undrained Tri-axial test was conducted on the unreinforced and reinforced samples where the behaviour of the samples were observed and compared. The results indicated that inclusion of fibres affects the soil’s undrained shear strength. It was observed that increasing the percentage inclusion increases the undrained shear strength of the soil, up to a certain amount. Further increment of fibres, however, does not show further improvement in the undrained shear strength.

Influence of Silica Fume and Additives on Unconfined Compressive Strength of Cement-Stabilized Marine Soft Clay

AbstractThis study presents results on the influence of silica fume (SF) and additives on the unconfined compressive strength (UCS) of ordinary portland cement (OPC)-stabilized salt-rich marine sof...

Experimental and numerical simulation research of the physical and mechanical properties of Attapulgite clay

<p indent=0mm>A series of laboratory experiments were carried out in this paper, around the problems of crusher sticking and tool wear in the pre-treatment of Attapulgite clay. Firstly, the results of mechanical experiments showed that the uniaxial compressive strength of Attapulgite clay decreases gradually with the increase of moisture content. And the triaxial test measured the elastic modulus of the Attapulgite clay to be <sc>0.98 GPa,</sc> the cohesive force to be <sc>2.40 MPa.</sc> Secondly, the meso-mechanical parameters of the numerical model were calibrated by the discrete element numerical experiment, with the condition of different moisture content, and compared with the laboratory test results to verify. Then the macro- and micro- mechanical properties of Attapulgite clay with different moisture content were deeply analyzed. As the moisture content content increases, the effective coordination number inside the sample decreases. The larger the moisture content, the greater the increase in porosity after loading, and the increase in porosity will result in the attenuation of macroscopic mechanical properties. The conclusions in this paper are helpful to optimize the industrial treatment process under different moisture content of Attapulgite clay.

Experimental Evaluation of Shear Strength of Kaolin Clay under Cyclic and Noncyclic Thermal Loading

Abstract The soil response to daily temperature variation imposed by an energy pile is critical for estimating the energy pile’s capacity and serviceability. It is, therefore, necessary to determine the temperature-induced effects on mechanical properties of soils. This article presents the results of an experimental study on the effects of thermal loading on shear strength of reconstituted kaolin clay. The study was performed using a triaxial testing apparatus capable of applying thermal loading. Different cyclic and noncyclic thermal loadings, with temperatures ranging between 24°C and 34°C, were applied. In addition, two theoretical mechanisms defining force distribution at the interparticle level were used to analyze the shearing behavior of clay under thermal loading. Both experimental and theoretical results indicate that the influence of temperature variation on the shear strength of clay is primarily controlled by stress state and stress history.

STRENGTH OF SOFT CLAY REINFORCED WITH 10 MM SINGLE CRUSHED COCONUT SHELL (CCS) COLUMN

Stone column can be used as a ground improvement technique where a portion of soft soil is replaced with granular material such as stone or sand. The benefit of using stone columns in low strength soil has been proven as an efficient method to improve the bearing capacity and reduce settlement of soft soils. This study aims to investigate the improvement in shear strength of soft clay by embedded with a single crushed coconut shell (CCS) column. The cost of soil improvement can be reduced because of CCS is a waste material. This paper was done by determining the physical and mechanical properties of kaolin and CCS as well as the effect of height penetration ratio of a single CCS column on shear strength characteristics. Unconfined Compression Test (UCT) was conducted for 4 batch kaolin samples including a control sample in order to determine the shear strength. Each batch involved four samples to find the accurate value. The research variables are the height of crushed coconut shell column which is 60 mm, 80 mm and 100 mm where the column penetration ratio is 0.60, 0.80 and 1.00 respectively. A total of 16 unconfined compression tests had been conducted on kaolin sample with dimensions of 50mm in diameter and 100 mm in height. The increment of shear strength by embedded with crushed coconut shell columns is 19.02 %, 34.76 % and 24.34 % for with 4 % area displacement ratio at column penetration ratio of 0.60, 0.80 and 1.00 respectively. From the results obtained, the relationship between shear strength increases is influenced by the height of the column. The maximum column height (full penetration) does not generate the highest strength and it proves that critical column length theory is true in this study.

Effect of dispersant on the tangential adhesion strength between clay and metal for EPB shield tunnelling

When Earth Pressure Balance (EPB) shields pass through clayey ground, the working tool is frequently clogged, causing a low tunnelling rate and accelerating cutter disk abrasion. Clay clogging is considered to be due to the high tangential adhesion strength between the clay and metal. This paper investigates the changes in the tangential adhesion strength with the consistency index under different total normal stresses and with different dispersant contents using a mixture of bentonite and kaolin (mass ratio of 1:1). The results showed that the tangential adhesion strength first decreased significantly and then remained almost constant with an increase in water content. Injection of the dispersant could decrease the tangential adhesion strength of clay. The tangential adhesion strength decreased gradually with a lower dispersant content (<4%) and then remained nearly unchanged. The tangential adhesion strength increased slowly with a consistency index lower than 0.5–0.6 and then increased significantly. Considering the effect of dispersant on the Atterberg limits of clay, the tangential adhesion strength between the soil and metal with different dispersant contents was virtually identical at the same consistency and under a normal stress. The tangential adhesion strength showed an exponential relationship with the normal stress and consistency index when the consistency index of clay was lower than 1. The reduction of average tangential adhesion strength showed a linear increase as that of liquid limit increased. The slope of the line increased when the normal stress increased. These results indicate that changes in the liquid can represent the effect of dispersant on the adhesion of clay. From the test results, it can be considered that a supporting medium with a consistency index lower than 0.5 is suitable for EPB shields. Since soil with a consistency index lower than 0.4 is easily squeezed out of a screw conveyor, a supporting medium with a consistency index of 0.4–0.5 is ideal for EPB shields, which is in agreement with the conclusion proposed by Hollmann and Thewes.

Triaxial Shear Test on Hydrochloric Acid-Contaminated Clay Treated by Lime, Crushed Concrete, and Super Absorbent Polymer

Acid pollution weakens the bearing capacity of subgrade, and discarded concrete occupies land. The mechanical properties of hydrochloric acid-contaminated clay were investigated by triaxial consolidation undrained tests. Also, the theory of diffusion double electric layer was employed to explain the change principle of cohesion and compression characteristics of hydrochloric acid-contaminated clay. In addtion, the curing effects of lime, crushed concrete, and SAP on the shear strength of hydrochloric acid-contaminated clay were compared. The triaxial test results show that cohesion decreased with the increase of hydrochloric acid concentration. The internal friction angle firstly increased and then decreased, and the change of internal friction angle was less affected by acid concentration. The curing effect of crushed concrete was similar to that of lime, which was better than lime. SAP could only improve the cohesion of the hydrochloric acid-contaminated clay; the internal friction angle decreased significantly; the three kinds of curing materials could significantly improve the cohesion of acid-contaminated clay to be higher than the natural clay, improving the shear strength to a certain extent. Additionally, the theory analysis illustrated that due to the change in the thickness of the diffusion layer between the clay particles, the van der Waals force between the particles changed, and the colloidal formation of the micelles led to changes in cohesion. The study can provide references to the treatment of contaminated soil in engineering practice.

Shear Strength of a Synthetic Transparent Soft Clay Using a Miniature Ball Penetrometer Test

This article is concerned with the properties of Laponite colloids, which are being used as a transparent surrogate for soft natural clays. Laponite is a synthetic smectite clay similar to natural hectorite clay that is made of magnesium lithium phyllosilicate (MLPS). The effect of aging on the shear strength of transparent soft clay formed from MLPS and water is presented in this article. A miniature ball penetrometer (MBP) was developed for this study. MBP tests were used to measure the shear strength of samples at three different concentrations of MLPS in water. Sodium pyrophosphate was used to slow down the flocculation of MLPS by altering its rheology, thus improving the transparency of higher MLPS concentration samples. Parameters that were studied included the water quality, aging, penetration rate, penetrometer geometry, and repeatability. The strength of clays made of MLPS was found to increase with MLPS concentration, depth, and penetration rate. Water quality had little effect on strength or transparency. Equations to predict the strength of MLPS based on constituents, age, and stress, as well as the effect of rate of loading, are proposed. The performance of the MBP test was also investigated. It showed excellent repeatability, although the shear strength measured was dependent, to some degree, on the penetrometer’s dimensions as well as the rate of loading.

Empirical Factors for Miniature Cone and T-bar Penetrometers for Kaolin Clay

Undrained shear strength is a key parameter of clay and is popularly determined by penetrometers. Miniature penetrometers are preferred to estimate the undrained shear strength of clay for small-size model tests. In order to estimate undrained shear strength, an empirical factor should be established to correlate the tip resistance to the undrained shear strength. However, published data on miniature penetrometers are limited. This paper aims to evaluate empirical factors on miniature cone and T-bar penetrometers using a cylindrical chamber. Kaolin clay specimens were prepared in the chamber under five pre-consolidation pressures to control their undrained shear strength. Two miniature cones with diameters of 10 mm and 16 mm and a T-bar penetrometer with 10-mm diameter and 40-mm length were used to investigate penetration rate, boundary, and empirical factor. Unconsolidated-undrained triaxial tests and vane shear tests were carried out to measure undrained shear strength. Finally, empirical factors for the penetrometers were constructed to correlate tip resistance to undrained shear strength. The empirical factors established at 20 mm/s of a penetration rate for 10-mm-diameter cone, 16-mm-diameter cone and T-bar penetrometer are 18.33, 13.09 and 12.5, respectively.

Determination of the shear strength of interlayer materials in a clastic rock Aera

This study focus on the influence of the shear strength in unsaturated soil under different matric suction. 12 groups of GDS tests under different conditions were executed to analysis the relationship between net confining pressure and deviatoric stress. Then, used the unsaturated soil strength theory to calculated the shear strength of the weak interlayer. The results show that under the same confining pressure and unsaturated conditions, the deviatoric stress increase as the matric suction increases. The total cohesive force and the matrix suction of a linear relationship during the test process, the growth of the slope angle for the matrix suction is 6.6°. Finally, a modified formula for shear strength of the soft sandwich silty clay in this landslide was proposed.

Undrained stability of unsupported rectangular excavations in non-homogeneous clays

Solutions for the undrained stability of unsupported excavations are important in practice as they can be used for assessing the safety of temporary excavations associated with various civil works. Even though the previous stability solutions of unsupported excavations namely infinitely long trenches and circular excavations are available in the literature, there is a lack of the stability solution of unsupported rectangular ones. In this paper, the lower bound solutions for the undrained stability of unsupported rectangular excavations in non-homogeneous clays are presented for the first time. A three-dimensional lower bound finite element limit analysis is developed in order to investigate the stability of this problem. The undrained shear strength of non-homogeneous clays are considered as a linearly increasing one with depth. The effects of aspect ratios of rectangular excavations, excavated depth ratios, and normalized strength gradients on the stability number of the problem and its associated failure mechanisms are examined parametrically. A new design equation of the problem is also firstly presented for practical use by practising engineers.